Addition-Fragmentation-Transfer Monitored by Fluorescence Lifetime Imaging Microscopy

Radically activated dynamic covalent bonds can enable reprocessable, thus more sustainable, polymeric materials, but conventional characterization approaches limit understanding of atomic-scale rearrangements. Specifically, the addition-fragmentation-transfer (AFT) pathway has been characterized by bulk-scale changes in mechanical properties; attempts to probe the exchange on a atomic scale are limited. Traditional spectroscopic methods cannot detect AFT because the overall bonding environment is unchanged before and after exchange with a very short-lived intermediate. To this end, this study uses fluorescence lifetime imaging microscopy (FLIM) to probe local AFT bond exchange via nondestructive characterization. Herein, allyl sulfide AFT in acrylate polymer thin films is monitored by FLIM over time, leveraging the sensitivity of fluorescence lifetime to nearby bond rearrangement through a series of control systems. Notably, FLIM reveals a continuing AFT cascade beyond the typical time scale when mechanical property change saturates. We anticipate applying these findings to other hard-to-access phenomena, as well as a mechanistic understanding of the environmental dependence of fluorescence lifetime.